She has always been in love with Scrooge, but he has never accepted
her love.
Back in 1898 he even presented her a very precious fur hat with the
agreement that she would leave him alone, but she broke her promise.
(When that story later was reprinted in the USA the year was changed
to 1928.)

In later stories she became a business-woman herself to try to beat
Scrooge in his own game.

Carl Barks once sent Scarpa a sketch
where Brigitta tries to seduce Scrooge by means of a money perfume.
Scarpa used that idea in 1976 in Zio
Paperone e il casco d'oro.
The original Barks sketch got lost, and was never printed anywhere
before it got lost.
Scarpa has tried to recreate it as close as he can and it is printed
in the Italian book on Scarpa by Luca Boschi, Leonardo Gori and Andrea
Sani, as well as in Uncle Scrooge 242.
(There is also another recreation of this sketch, also by Scarpa,
printed in the French Picsou Magazine - 60° anniversaire de
Donald.)